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  • Cloud water interception in the temperate laurel forest of Madeira Island
    Publication . Figueira, Celso; Sequeira, Miguel Menezes de; Vasconcelos, Rita; Prada, Susana
    A cloud belt frequently forms on the windward side of Madeira Island, between 800 and 1600 m a.s.l., as a result of adiabatic cooling of the northeastern trade winds that are forced upward. Temperate laurel forest is the most common vegetation inside that cloud belt altitudinal range. Cloud water interception was estimated by comparing precipitation and throughfall during a hydrological year. It totalled 200 mm (8% of rainfall) during 65 days (3 mm d-1) and seems to constitute a larger fraction of water input during drier months. Multiple linear regression between gauge standard deviation and throughfall throughout rain events shows that cloud interception is common before the onset of rainfall. Its role in the ecohydrology of laurel forest and in the island’s hydrology should be acknowledged. Further studies on this issue should be a priority in order to better understand these dynamics and provide tools for the correct management of this protected forest and the island’s groundwater resources.
  • Cloud water interception in the high altitude tree heath forest (Erica arborea L.) of Paul da Serra Massif (Madeira, Portugal)
    Publication . Prada, Susana; Sequeira, Miguel Menezes de; Figueira, Celso; Vasconcelos, Rita
    Cloud water interception (CWI) occurs when cloud droplets are blown against the forest canopy, where they are retained on the vegetation surface, forming larger water droplets that drip into the forest floor. CWI was measured from 1 October 1997 to 30 September 1999, on a first-line tree heath (Erica arborea), at Bica da Cana, Madeira Island. Rainfall was corrected for wind-loss effect and compared with throughfall and other climatological normals. The CWI depletion rate along a forest stand transect was also analysed during three distinct fog events in 2008. Cloud water was 28 mm day 1, corresponding to 68% of total throughfall and 190% of the gross precipitation. Cloud water correlates directly with monthly normals of fog days and wind speed and correlates inversely with the monthly air temperature normal. CWI has an exponential correlation with monthly relative humidity normal. Cloud water capture depletion along the stand shows a logarithmic decrease. Although a forest stand does not directly relate to a first-line tree heath, this study shows that CWI is a frequent phenomenon in the Paul da Serra massif. Restoration and protection of high altitude ecosystems in Madeira should be a priority, not only for biodiversity, ecological and economical purposes but also for its role in regional water resources.
  • Fog precipitation and rainfall interception in the natural forests of Madeira Island (Portugal)
    Publication . Prada, Susana; Sequeira, Miguel Menezes de; Figueira, Celso; Silva, Manuel Oliveira da
    Situated in the Atlantic Ocean, Madeira is a within-plate volcanic island, approximately 600 km northwest of the Western African coast. Cloud cover formed mainly of orographic origin persists on Madeira for more than 200 days per year between 800 m and 1600 m altitude. Since vegetation occupies 2/3 of the island’s surface, fog precipitation, which occurs when fog droplets are filtered by the forest canopy and coalesce on the vegetation surfaces to form larger droplets that drip to the forest floor, is an important hydrological input. Rainfall interception and fog precipitation data were collected between 1996 and 2005 in the natural forests of Madeira. Six throughfall gauges were placed under the canopy of three different types of forest: high altitude tree heath forest (1580 m), secondary tree heath forest (1385 m) and humid laurisilva forest (1050 m). Fog precipitation is higher under high altitude heath forest (average canopy interception was 225% of gross precipitation) and dependent both on altitude and vegetation type, due to different tree architecture and leaf shape. Although results are conservative estimates of fog precipitation, they point towards the importance of fog-water as a source of groundwater recharge in the water balance of the main forest ecosystems of Madeira.
  • Response to “Comment on fog precipitation and rainfall interception in the natural forests of Madeira Island (Portugal)”
    Publication . Prada, Susana; Sequeira, Miguel Menezes de; Figueira, Celso; Prior, Víctor; Silva, Manuel Oliveira da
    In this paper we discuss the comments given by Regalado and Ritter (2010) on our previous work (Prada et al., 2009). Here, we demonstrate that rainfall correction does not significantly change the results; make clear why Site 1’s fog precipitation values do not seem to be overestimated due to the low number of gauges; present observational evidence that suggest high water yields in Site 1; and why we consider that fog water may be important for groundwater recharge. We also review different methodological, ecological and climatic factors between Madeira and the Canary Islands’ fog precipitation studies that might explain different values between them (Ritter et al., 2008, 2009).